The present invention pertains to methods for preventing flaking of metals or metal-derived materials from interior surfaces of a sputter apparatus during a sputter process. More specifically the invention pertains to pasting methods for sputter apparatus that use non-planar sputter targets.
Magnetron sputtering is often used to coat substrates with materials. Magnetron sputtering is particularly useful because higher sputter rates can be achieved relative to sputtering methods that do not use magnetic fields. Magnetron sputtering is particularly useful for integrated circuit fabrication, more specifically depositing thin films onto semiconductor substrates.
Traditionally, a planar target made of a particular metal, alloy, or other conductive material is used as a source of material to be sputtered onto a substrate. During sputtering, the target serves as a cathode in an electrical circuit, and a magnetic field is established for confinement of electrons (from the target) near the target surface. This magnetic confinement greatly increases the possibility of ionizing collisions and thus the sputter rate. In conventional systems, a fixed magnetic field configuration is used.
A significant problem that arises in magnetron sputtering is build-up and flaking of sputtered material from interior surfaces of sputter apparatus to substrates within the sputter apparatus. This is particularly problematic in semiconductor fabrication. For example a metal target is used for sputtering a metal nitride onto a wafer. The target is sputtered in the presence of a small amount of nitrogen gas to produce the metal nitride in-situ during sputtering. Over time, metal nitride is deposited on, for example, shielding plates within the sputtering process chamber. Inherent stress in the deposited film of metal nitride causes it to flake off. When this flaking occurs during a sputter process, the substrate is contaminated with the particles of metal nitride, damaging delicate circuitry.
One method to control flaking is termed xe2x80x9cpasting.xe2x80x9d For example, with respect to a metal nitride flaking problem as described above, periodically a layer of the target metal is sputtered over metal nitride material deposited on process chamber interior surfaces in order to encapsulate the metal nitride. When planar targets are sputtered, full-face erosion of target material from the targets"" planar surface is typically achieved, that is, during sputtering target material is evenly removed from the target surface and no material is re-deposited onto the target. In such examples, only deposited material on surfaces other than the target require encapsulation.
More recently, non-planar targets have found use in magnetron sputtering. For example, in hollow cathode magnetron (HCM) sputtering, cup-shaped targets are used. With non-planar targets such as these, fixed magnetic field configurations often cause uneven erosion profiles on the target surface due to the variation in the target sputter surface. During sputtering, sputtered material is re-deposited onto some target surface areas where the magnetic field configuration does not permit erosion. Flaking of re-deposited material from such areas of non-planar targets is problematic. Traditional pasting methods do not prevent flaking from these target areas.
What is needed therefore are improved methods of preventing flaking of metals and metal-derived materials from interior surfaces of a sputter apparatus during a sputter process. More specifically, methods that prevent flaking from non-planar sputter targets as well as other interior surfaces of sputter apparatus that use such targets.
The present invention pertains to methods for preventing metal or metal-derived material from flaking during sputter processing of substrates. Methods of the invention are particularly useful for non-planar sputter targets. The magnetic field configuration in a sputter apparatus is modulated during a pasting process. Flaking from regions of the target, shield, or other internal components of the sputter apparatus is inhibited by pasting methods which include encapsulation and optionally removal of material, for example by erosion via high density plasma.
Thus one aspect of the invention is a method of preventing a metal or a metal-derived material from flaking from a surface within a sputter apparatus during a sputter process that uses a non-planar target. Such methods may be characterized by modulating the magnetic field configuration in the sputter apparatus during a pasting process. Preferably modulating the magnetic field configuration in the sputter apparatus during the pasting process includes pasting using a first magnetic field configuration; and pasting using a second magnetic field configuration. Preferably each of a plurality of electromagnetic coils used for pasting using the first magnetic field configuration have the same polarity as when used for the sputter process. In preferred embodiments, the order of pasting process elements is interchangeable. In a particularly preferred embodiment, the pasting process begins with pasting using the second magnetic field configuration, followed by pasting using the first magnetic field configuration. In this way, once the pasting process is complete, apparatus are more readily configured to continue the sputter process as before. Preferably, the second magnetic field configuration is produced by changing the polarity of at least one of the plurality of electromagnetic coils used for pasting using the first magnetic field configuration.
Preferably the second magnetic field configuration is used to create a high-density plasma at a region of the non-planar target where a deposit of a sputtered material exists, the deposit created during a previous sputter process. In some embodiments, the second magnetic field configuration is used to create a high-density plasma at a region of the non-planar target where a deposition-erosion boundary exists, the deposition-erosion boundary created during a previous sputter process.
Preferably pasting using the first magnetic field configuration takes between about 60 and 200 seconds, more preferably about 120 seconds; and pasting using the second magnetic field configuration takes between about 10 and 60 seconds, more preferably about 20 seconds.
Preferably the metal includes at least one of tantalum, titanium, tungsten, copper, cobalt, molybdenum, zirconium, chromium, and alloys thereof. Preferably the metal-derived material is a metal nitride. Metal nitrides of the invention preferably include at least one of tantalum nitride, titanium nitride, and tungsten nitride.
Preferably the sputter process is used to deposit the metal-derived material sequentially on a plurality of semiconductor wafers and the pasting process is repeated after between about 25 and 500 wafers have been exposed to the sputter process, more preferably between about 200 and 500 wafers. Put another way, preferably pasting methods of the invention are performed after the target has been used for between about 10 and 200 kWh, more preferably between about 80 and 200 kWh.